The present invention relates, on the one hand, to an artificial grass mat comprising a ground fabric and a number of artificial grass blades protruding from the ground fabric. On the other hand, the present invention relates to a method for the production of an artificial grass mat of this type.
Artificial grass mats are increasingly being used to replace natural grass because:                climate conditions are not always suitable for natural grass;        loads which are imposed on natural grass (for example when practising sport) damage the ground, so lengthy intervals are necessary before the ground can be used again;        natural grass is obviously high-maintenance.        
It is generally known to produce artificial grass mats by connecting plastics material grass fibres to a support material, the plastics material grass blades protruding preferably perpendicularly from the supporting fabric. The plastics material grass blades are usually hard and smooth plastics material fibres such as polyolefins (polyethylene, polypropylene and blended forms) or polyamides.
Usually, the support material is a textile cloth through which the plastics material grass blades are tufted. In other words, a plastics material grass fibre is pressed through the cloth by means of a needle, thus forming a loop. On the other side of the textile cloth, a hook takes over the loop formed and brings this loop to the desired height. Subsequently, the loop is usually cut through, thus forming two upright grass blades. The support material can be woven, knitted or a nonwoven.
Instead of tufting the plastics material grass blades through the support material, they can also be produced as a pile in a pile fabric or pile knit.
However, in the production of textile cloths, the yarns, and in particular the pile yarns, are the most expensive part of the product. Solutions which yield the same performance levels while consuming fewer yarns are thus economically very beneficial solutions and solutions which yield higher performance levels while consuming the same number of yarns are industrially very beneficial solutions.
International patent application WO 2004/057111 describes the improvement to spread the artificial grass blades equally in the artificial turf mat during tufting by selecting the distance between the pile rows and the distance between piles in a single row so as to be approximately equal and, in addition, setting this distance to at least 10 mm. This is to prevent the studs on the boots of, for example, footballers from becoming caught in the pile yarns and also to be able easily to release the filling in order to prevent compression of the filling.
This means that merely a limited number of pile tufts have to be used: for 10 mm×10 mm, there are at most 10,000 pile tufts/m2 and in the preferred embodiment of 13 mm×13 mm, there are at most 5,900 pile tufts/m2; in a further preferred embodiment of 16 mm×16 mm, there are just 3,900 pile tufts/m2.
During the tufting of artificial grass, it is therefore known to use mainly relatively thick filaments in order to arrive at a good degree of pile occupation. For this purpose, mainly polyethylene and polypropylene yarns are used as fibrillated strip yarns or as bundled monofilaments having a fibre density of between 6,000 and 14,000 dtex, 10,000 to 14,000 dtex usually being used for football applications (density of 10,000 dtex=1,000 tex means that the fibre or the yarn has a weight of 1,000 g per km of length). That is to say, artificial grass should be used to create a state in which the density of the artificial grass blades has an attractive appearance and, for example for sport applications, the artificial grass blades can support a ball effectively.
A combination of tuft/burl density and the density of artificial grass blades which, in turn, usually consist of a number of relatively thin fibres or monofilaments which are bundled to form a plastics material yarn determines the behaviour of a ball rolling on an artificial grass mat.
Tuft densities are characterized by two parameters:                the density of the tufting needles in the needle block. This parameter is expressed as the gauge having the following conventional values: ¾″ or ⅝″ for one needle per 19 mm and per 15.8 mm respectively or, put differently, 52 and 63 needles and thus tuft rows per metre respectively;        the density of the stitches per length of unit characterizes the density in the other direction and is between 10 and 20 per 10 cm, usually 13 to 16 per cm, corresponding to: 100 to 200 pile tufts per metre and usually 130 to 160 pile tufts per metre (or, put differently, gaps between 10 and 5 mm and 8 and 6 mm respectively). Per m2, this yields a number of pile tufts of between 5,200 and 12,600 and usually between 6,760 and 10,000 tufts/m2.        
It will be clear from the foregoing that the limitations, known in tufting practice, in the density of needles and in the limited density of artificial grass pile make it difficult to achieve the balance proposed in WO 2004/057111 between the number of tufts per metre in one direction and the number of tufts per metre in the other direction. That is to say, relatively high densities, both for the needles and for the stitches, present in these types of yarns a problem as a result of the heating of the needles in the tufting process. Pile tufts heavier than the specified 14,000 dtex also present a problem to the needles in the tufting process.
This limitation of tuft density and fibre density limits the possibilities of the further improvement to the properties of artificial grass using the tufting process.
The patent Applicant saved considerable amounts of raw materials by weaving artificial grass with 16,000-dtex pile yarns (bundle of 8 2,000-dtex filaments) in a 7/16 W weave structure. The patent Applicant thus achieved the advantage that each pile burl has two pile legs which are set apart from each other over 8 picks, and this usually amounts to ±16 mm from each other. As a result, the pile yarns (16,000 dtex) behave in a theoretically equivalent manner to tufted pile yarns having a density of 8,000 dtex but double in number, because the tufting process entails that the two pile legs are at all times directly next to each other.
However, practical experience teaches that both in terms of appearance and in terms of properties, a woven artificial grass mat comprising 5,000 pile burls (each having two pile legs) having a density of 16,000 dtex behaves at least as well as a tufted artificial grass mat comprising 8,400 12,000-dtex tuft burls (each having two tuft legs). The improved spread of the pile legs in the desired artificial grass mat thus yields a considerable advantage in terms of the saving of raw materials, in the aforementioned case 20%.
A drawback of both the weaving and the tufting of artificial grass using pile yarns having densities of 6,000 and higher is that during the replacement of bobbins the pile yarn of the new bobbin must be linked e.g. by knotting to the pile yarn of the old bobbin and that the linking of “thick” pile yarn strips or filament bundles of this type is difficult, time-consuming and labour-intensive. In addition, the knots have large dimensions and can thus cause manifold disturbances in the weaving or tufting process.
Furthermore, a knot in pile yarns like this, when jammed (for example as a result of a knot which becomes stuck) stop the machine only when the pile yarn breaks. In order to break through pile yarns of this type, a very high degree of force must be applied, as a result of which machine components or harness components, such as for example headles or bobbin spindles in the weaving creel, are often also sollicitated by high loads and undergo deformation or break. This causes additional problems, downtimes and intervention costs.
Furthermore, in order to achieve a high degree of autonomy of the weaving—or tufting machine, the bobbins comprising these highly thick pile yarns must be suitably heavy to be able to produce a considerable fabric length before replacing the bobbin. This makes it more difficult to carry out the supply of the yarns in the weaving creel.
The object of the invention is to find an artificial grass mat and a method for the production of a woven artificial grass mat in which the pile yarn is distributed more uniformly over the artificial grass mat and preferably yields material saving (especially in pile yarns) while at the same time maintaining comparable performance levels to or even obtaining better performance levels than the artificial grass mats according to the prior art. A further object of the invention is to simplify the work surrounding the weaving device to which the method is applied and to obtain a weaving device which operates more quietly and fewer downtimes during weaving.
The object of the invention is achieved by providing an artificial grass mat comprising a ground fabric and a number of artificial grass blades protruding from the ground fabric, at least one of the artificial grass blades being formed from a pile-warp yarn having a density of less than 5,000 dtex and the artificial grass blades being distributed over the aforementioned grass mat in the form of rows, spread over the weft direction, of artificial grass burls which succeed one another in the warp direction, the artificial grass blades protruding from the ground fabric forming pile legs of the artificial grass burls which are bound in the ground fabric over opposing weft yarns in a W bond.
In a preferred embodiment at least one of the artificial grass blades is formed from a pile-warp yarn having a density of less than or equal to 4,000 dtex, more particularly less than or equal to 3,000 dtex and most particularly less than or equal to 2,000 dtex. It will be clear that all artificial grass blades in the fabric according to the invention can have a density of less than 5,000 dtex or less than one of the other aforementioned densities.
According to a preferred embodiment of the artificial grass mat according to the present invention, the aforementioned artificial grass mat comprises at least 20,000 artificial grass burls per m2. Preferably the artificial grass mat comprises at least 30,000 artificial grass burls, more particularly the artificial grass mat comprises at least 40,000 artificial grass burls and in a most particular embodiment the artificial grass mat comprises at least 50,000 artificial grass burls per m2.
In the artificial grass mat according to the invention, each artificial grass burl comprises preferably two pile legs, each artificial grass burl between its two upright legs being bound at least three times over weft yarns in between of them. This has the advantage that each pile leg is bound around different wefts, both of which are located between the two upright pile legs. In particular each artificial grass burl between its two upright legs is bound five times over well yarns in between. More particularly each artificial grass burl between its two upright legs is bound seven times over well yarns in between.
In a most preferred embodiment of the artificial grass mat according to the invention the distance between two pile legs, which succeed each other in the warp direction, of a different pile-warp yarn is less than the distance between two pile legs, which succeed each other in the warp direction, of a single artificial grass burl.
According to a particularly advantageous embodiment of the artificial grass mat according to the invention at least one of the artificial grass blades protruding from the ground fabric is a monofilament yarn, meaning not a bundle of a plurality of filaments or yarns. According to a more particular embodiment of the artificial grass mat in addition to the artificial grass blades protruding from the ground fabric, at least one shrinkably textured yarn also protrudes from the ground fabric. Textured yarns of this type are made of polyethylene or polyamide and shrink after cutting-through and/or heating and thus act as a filling yarn in the artificial grass mat. These filling yarns support, on the one hand, the cut pile and have, on the other hand, the function of maintaining any filling of the artificial grass mat and preventing excessive compaction of this filling. Furthermore a filling yarn of this type can contribute to the damping of a ball strike or to the replacement of conventional fillings in artificial grass.
According to a most particular embodiment of the artificial grass mat according to the present invention the aforementioned grass mat is woven using a double-face weaving method.
Another subject-matter of the present invention relates to a method for the production of an artificial grass mat comprising a ground fabric and a number of artificial grass blades protruding from the ground fabric. According to the invention a bottom and a top fabric are woven using a double-face weaving method, the fabrics consisting of weft yarns, ground-warp yarns and grass blade-forming pile-warp yarns, thus forming alternately in both fabrics artificial grass burls each having two pile legs, at least one of the grass blade-forming pile-warp yarns having a density of less than 5,000 dtex and the grass blade-forming pile-warp yarns being interlaced over the weft yarns according to a W weave structure.
According to a particular method for the production of an artificial grass mat the grass blade-forming pile-warp yarns in the weft direction are distributed over a number of pile-warp systems, each pile-warp system comprising a number of grass blade-forming pile-warp yarns which are interlaced according to a W weave structure and the various aforementioned pile-warp yarns within a single pile-warp system being offset with respect to one another in the warp direction. This has the advantage that the pile legs of the artificial grass burls formed are much more spread over the artificial grass mat.
According to a more particular method according to the invention in at least one pile-warp system each weft yarn which is located with respect to a tight warp yarn on the back of the artificial grass mat is bound by at least two grass blade-forming pile-warp yarns, each of these two pile-warp yarns placing one pile leg each on a different side of the weft yarn.
According to a most particular method according to the invention there extend in each pile-warp system six grass blade-forming pile-warp yarns which are interlaced according to a 5/12 W weave-structure and which within a single pile-warp system are each offset over the two picks respect to one another.
In another preferred method according to the invention there extend in each pile-warp system six grass blade-forming pile-warp yarns which are interlaced according to a 7/16 W bond and which within a single pile-warp system are each offset over four picks with respect to one another.
According to a particularly preferred method according to the invention weaving is carried out in phase opposition, so in the shed formation for each rising pile-warp yarn a different pile-warp yarn at the same time falls over the same distance.
In order further to illustrate the features of the present invention and in order to indicate additional advantages and particularities thereof, there will now be described in greater detail an artificial grass mat according to the invention and the method for the forming of a grass mat of this type. It will be clear that nothing in the following description may be interpreted as a limitation of the protection for the invention sought in the claims.